To navigate a navigable navigable to a
URL url using an optional Document-or-null sourceDocument (default null), with an optional POST
resource, string, or null documentResource (default null), an optional boolean exceptionsEnabled (default false):
Let sourceSnapshotParams be the result of snapshotting source snapshot params given sourceDocument.
Assert: documentResource is null if and only if response is null.
Let traverseQueue be a new session history traversal queue.
Append the following session history traversal queue steps to traverseQueue:
Let changingNavigableContinuation be the result of starting an unload given sourceSnapshotParams.
Queue a global task on the navigation and traversal task source given navigable's active window to run the remaining steps in parallel.
Append session history traversal steps to traverseQueue to finalize a cross-document navigation given navigable.